WATCH: SHAWN MENDES, NIALL HORAN Jam To “Mercy”!

For star-studded event like the American Music Awards, a lot of things can definitely happen. But who would have ever imagined that a backstage duet of two teen superstars would transpire casually? It's not just your ordinary impromptu performance as you can actually feel their emotions while singing the song. No mercy on our feelings, Shawn and Niall. Watch the video below: